The present invention relates to a heating apparatus for electric ovens, gas ovens and ovens of the type combining the former types.
Recent developments in the field of semiconductor technology have made possible the mass production of inexpensive large-scale integrated circuits and have rapidly facilitated the use of electronic devices for the control units of equipment for civilian use (home appliances). The control panel of a heating apparatus equipped with an electronic control unit is generally constructed as follows. The control panel includes function selecting means for selecting one of a plurality of functions, numeric value input means for supplying the time or numeric value corresponding to the selected function and display means for displaying the time or numeric value. More specifically, the function selecting means may for example be comprised of a plurality of output keys for selecting a desired one of a plurality of heat outputs. Assuming that the desired one of the plurality of outputs is selected, there is still the problem of the construction of the numeric value input means. In the case of this example, the heating time must be supplied as the next step. Probably, a rotary timer is the means capable of most rapidly setting the heating temperature with little danger of making a erroneous setting. While one should not undoubtedly overlook the fact that the users have heretofore accustomed themselves to using rotary timer, its advantage that the heating temperature can be set by a "single twist" of the knob is still noteworthy. However, due to its analogic nature, the rotary timer has not been readily adapted for use with digital control systems and has not been used widely due to the need for new or improved A/D converters.
The numeric value input means used most widely with digital control systems are probably those which employ 10 numerical keys (0 to 9). In the case of these ten-key systems typified by electronic calculators, a numeric value is inputted in the order of the keys depressed while making a shift from a lower digit to a higher digit upon each depression. Thus, to input a heating time having a four-digit value, it is necessary for example to depress four of the numerical keys. As a result, it is impossible to determine the digit in which the first-depressed value is set until the depression of the numeric keys is completed. In other words, if the keys 1, 5 and 3 are inadvertently depressed in this order instead of depressing the keys 1, 5, 3 and 0 so as to input a heating time of 15 minutes and 30 seconds, a heating time of 1 minute and 53 seconds will be set. The provisions of the 10 numerical keys in addition to the function keys associated with the previously mentioned selection of functions greatly complicates the arrangement on the control panel and this places a burden on the user in searching for the desired key to depress. Furthermore, the large number of keys involves a considerable danger of depressing the adjacent keys by mistake. While such erroneous setting and erroneous operation can be tolerated as computing errors in the case of electronic calculators, in the case of a heating apparatus they will cause overheating of an object to be heated and hence the possibility a grave accident such as the production and breaking out of a fire causing the user to be burned.
With a view to decreasing the number of numerical keys and reducing the possibility of such erroneous setting, a method has been proposed in which the corresponding digit numerical keys are provided for the respective digits of a display unit. For example, in the case of a 4-digit display unit, four digit numerical keys are provided for the four digit places. For example, the four keys respectively correspond from top to bottom to "10 minutes digit", "1 minute digit", "10 seconds digit" and "1 second digit" and thus any numeric value can be entered into each of the digits. It is so arranged that the numeric value to be entered can be entered by repeatedly depressing the corresponding key a desired number of times or by automatic increments made so long as the key is depressed continuously, and it is only necessary to release the key upon entering the desired numeric value. FIG. 3 shows the operations required for setting a heating time of 15 minutes and 30 seconds.
This digit numerical key system is advantageous in that the correspondence between the display unit and the keys is very clear as will be seen from FIG. 1, that the possibility of erroneous setting is reduced greatly as compared with the 10-key system, that the number of keys can be reduced, that the danger of erroneous depression is reduced due to the provision of the numerical keys in a zone different from that of the function keys, that the hardware of the control system can be simplified and so on. However, this system is disadvantageous in that as compared with the previously mentioned rotary timer, the operating feeling is quite different causing a feeling of strangeness on the part of the user and that it is difficult to correct any excessively advanced numeric value. For instance, assume that a number "6" is erroneously set in the minutes digit in which "5" is to be set. In such a case, the correction requires to clear the number entirely by an erase key and then make the setting all over again. Alternatively, it is conceivable to connect each of the digit displays to a scale-of-six or decimal ring counter such that the occurrence of any overflow does not result in a carry to a higher digit. Thus, if the number "6" is set erroneously, the minutes digit key is continuously depressed to advance the count--"9".fwdarw."0".fwdarw."1".fwdarw.--until the number "5" is set again. However, this requires considerable time and moreover the user inevitably has a feeling of strangeness since the count is returned to "10 minutes" after the display of "19 minutes".
It will be seen from the foregoing that the known numeric value input means of heating apparatus still leave considerable room for investigation and thus there exists a need for a numeric value input means which is easy to operate, has less danger of erroneous operation, requires less time for setting and is excellent from the standpoint of safety.
It is therefore the object of the present invention to provide an improved numeric value input means for heating apparatus equipped with a digital control unit, which is operable with a feeling close to that of the prior art rotary timer and which has less possibility of giving a strong feeling of strangeness to the user, thereby preventing the occurrence of overheating due to any erroneous operation and reducing the operating time by providing the numeric value input means with a "setback" function.
It is another object of the present invention to provide an improved numeric value input means for heating apparatus, which is comprised of only a single operating knob thus relieving the user of his burden of looking for the desired key as in the past and which is furthermore physically separated from various other keys forming function selecting means, thus practically completely eliminating the possibility of erroneously operating the one of the two.
It is still another object of the present invention to provide such numeric value input means which can also be used skillfully for both time setting and temperature setting purposes.